Military personnel exposed to combat-related traumatic events, particularly those who develop posttraumatic stress disorder (PTSD), have a higher incidence of problematic drinking. However, little is known about the relationship between trauma, PTSD, and drinking in emerging adults (ages 21-30 years), in spite of this age group being at highest risk of developing subsequent drinking problems. The proposed clinical laboratory project will use a three group design. The target OIF/OEF population will have no trauma exposure [Control group], combat trauma exposure without PTSD [TE group], and combat trauma exposure with PTSD [PTSD group]. The type of traumatic event exposure history included will be limited to combat- related traumatic events that are interpersonal in nature. This project will use a well-established clinical laboratory paradigm of stress induction employed by our group, the Trier Social Stress Test (TSST), to investigate the role of a history of exposure to combat trauma on reactivity to the TSST and on stress- induced voluntary drinking. Subjects will not meet diagnostic criteria for alcohol dependence. Half of each group will receive the TSST and the other half will be randomized to the no stress condition. Using subjective as well as biological indices of stress, the first specific aim examines the effect of combat trauma history on stress reactivity, using subjective, neuroendocrine, and physiological measures of stress. The second specific aim will examine the effect of combat trauma history on subsequent drinking behavior and subjective response to alcohol using established procedures in a clinical laboratory paradigm. Exploratory analyses will also be conducted to examine the correlation between combat trauma history group and subjective response to stress, and combat trauma history group and drinking. Two additional exploratory analyses will evaluate the effect of the personality trait of distress tolerance (high and low), and the effect of carrying the 'S' or the rare 'LG' allele of the 5-HTTLPR polymorphism on the stress response and on voluntary drinking following stress induction. This study will advance our understanding of the relationship between a history of combat-related traumatic events, stress, and drinking. The ultimate goal of this line of research is to identify at risk groups early in their drinking careers, before unhealthy drinking practices and/or dependence develop. This information has the potential to inform prevention and intervention alcohol research.